1. Field of the Invention
The present invention relates to an electrostatic image developing toner, more specifically, an electrostatic image developing toner having excellent low-temperature fixability and hot-offset resistance and high followability of gloss to paper even in the coexistence of a vinyl resin and a polyester resin.
2. Description of Related Art
In electrophotographic image forming apparatuses, electrostatic image developing toners (hereinafter, also simply referred to as “toners”) that can be thermally fixed at a lower temperature are demanded for energy saving in, for example, a high-speed image formation and a low environmental load.
A decrease in fixing temperature of a toner requires a reduction in melting temperature or melt viscosity of the binder resin contained in the toner. A decrease in the glass transition point (Tg) or molecular weight of the binder resin for reducing the melting temperature or melt viscosity of the binder resin, however, decreases the thermal storage stability of the toner.
It has been accordingly proposed to use both a styrene-acrylic resin and a polyester resin, which gives an advantage of easily reducing the softening point while maintaining the high glass transition point (for example, see JP 2013-254123).
Although the coexistence of a vinyl resin, such as a styrene-acrylic resin, and a polyester resin gives low-temperature fixability, the vinyl resin and the polyester resin differ from each other in the melting rate at the time of fixing; hence a difference in gloss between the resins occurs after fixing, failing to provide high gloss to the images. In formation of an image on paper having high glossiness, such as coated paper or art paper, since the gloss of the image is lower than that of the paper, the image gives depressive impression to deteriorate the image quality and texture.
In order to form a high gloss image, it has been proposed to control the contents (contained amounts) of aluminum and tin in a toner to specific amounts (for example, see JP 2009-122522). However, such mere control cannot provide low gloss to images formed on paper having low glossiness, such as rough paper.
In order to reduce the gloss of an image, it has been proposed to use both a styrene-acrylic resin and a polyester resin and further adjust the net intensity of aluminum in the toner within a specific range (for example, see JP 2015-148724).
However, such a proposed Net intensity ratio of aluminum to tin causes a large difference in melting rate between the styrene-acrylic resin and the polyester resin, failing to form high gloss images on high gloss paper.